Riyad as-Salihin 796
The Book of Dress
The Description of the Length of the Qamees' Sleeves, the End of the Turban, and Prohibition of Wearing Long Garments Out of Pride and Undesirability of Wearing Them Without Pride
Abu Hurairah (May Allah be pleased with him) reported: The Messenger of Allah (ﷺ) said to a man who was performing Salah while his lower garment was trailing, "Go and perform your Wudu' again." The man went and came back having performed it. The Messenger of Allah (ﷺ) said (again), "Go and perform your Wudu'." Someone present said to the Messenger of Allah (ﷺ): "O Messenger of Allah! You ask him to perform his Wudu' and then you kept silent (without saying the reason for it)." He (ﷺ) said, "He performed Salah while his lower garment was below his ankles. Allah does not accept the Salah of a man who trails his lower garment." [Abu Dawud].